Clean flat mesh surface
The surface is uneven, because the vertices are arranged in such a way, that the faces are bent.
You can fix this by manually adjusting all the vertices to create the cleanest shape possible.

With the Subsurf Modifier enabled, you can barely spot the problem even with wireframes.
The uneven vertices are hard to spot.


Without Subsurf, the mistakes are visible. (Note that my example is very exaggerated, but the random offset of the five vertices is still not much.)


You can try and clean up your mesh, by going through all the vertices, and adjusting them manually from each angle. This can take more than one pass.

It will be easier if you use cleaner topology. When modeling with quads, it is advisable to make the faces as even and as square as possible.

In your mesh the faces resemble rectangles. Hence a just a slight variation of the vertices of the edge loop will make the surface seem distorted.


Try to have all edges similiar lengths, when modeling a single bent surface. (Of course once you want sharp angles, ridges, etc. this won't apply.)


You can achieve more even quads, by deleting some existing edge loops, which aren't necessary for the shape and add edge loops perpendicular to the previous. 

With Subdivided Surfaces, you only need four vertices for a cirle. Keep topology rich in information, low in detail.